Tonight I tried my best to take some night landscapes in the darkest of dark conditions. Hoping for an epic composition of the Milky Way and a landmark.

Of course, none of my glass could auto focus with nothing more than dots in the sky to lock on. I seemed to have the most success by lining up the infinity focus mark on the focus window, however, the 50mm 1.8 has no focus window.

How can I set (guess) focus on a lens in relatively complete darkness?

Looking though the viewfinder I see nothing but black. I tried using Live View function to set focus, but that's not helpful either. I'm shooting wide open at f/2.8 or f/1.8 to gather the most amount of light in the shortest exposure, so the DoF is short, and the focus needs to be on.

Added for clarity: looking though the viewfinder I see nothing but black. I tried using Live View function to set focus, also, shooting wide open at 2.8 or 1.8 to gather the most amount of light in the shortest exposure so DoF is short, focus needs to be on.
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Canon GangstaAug 1 '10 at 7:43

15 Answers
15

In the daylight focus on a very, very far away object, like a radio tower. Mark your focusing ring with a bit of tape or something, and you have your infinity setting.

For closer focusing in the dark carry a laser pointer. Tape it to the camera or tripod so it points at your subject. The red dot should be easily seen through the viewfinder, and it will be easy to tell if you've got it in focus or not. You will probably have to use manual focus. Turn off the laser when taking the photo.

The marking tape idea doesn't work if you have an internal focusing lens like the Sony E-mount 18-105. The focusing ring smoothly rotates without reaching an end-point.
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Kartick VaddadiJun 10 '14 at 7:18

Many suggested answers so far assume that you can see something through the viewfinder or the focal point is close enough to use a focusing aid. While all great suggestions for low light focusing, I think you're dealing with no light focusing.

I spend a lot of time photographing similar situations where there is just no light in the viewfinder at all. The method I use to focus in these situations is trial and error. I start by setting the lens to infinity focus, capture a frame, check focus, adjust if necessary and take another exposure. If you're taking 10 minutes exposures, this can be time consuming, in my case I up the ISO for the focus exposures then lower it for the keepers.

Trial and error is probably not the answer you're looking for, but it's worked for me for years. I haven't found a better method of setting focus in zero light.

Your "no light focusing" is really just an extreme of "low light focusing". If there were truly no light, any picture you take would be black except for noise and dead pixels.
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Evan KrallFeb 20 '11 at 6:58

2

Technicalities aside, Evan. One thing is that if the Moon is present, I've used that to focus on the sky then move the camera back into position.
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Nick BedfordFeb 20 '11 at 8:07

@Evan-- I've used this approach for night shots as well. Typically, I can see nothing through the viewfinder, but on the back after a 5min exposure (for instance), something is visible.
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mmrJun 9 '11 at 14:57

If you want to focus on the stars there are many ways to accomplish this.

A few possibilities are:

A right angle finder with magnification (I've used a Hoodman with 2.5x magnification). Choose a bright star to focus on.

A Hartmann or Bahtinov mask (can be generated online here and here). This is basically a piece of cardboard or plastic with a certain pattern cut out that will aid during focussing. Using a right angle finder with magnification in combination with a mask for the best results. If the stars are still to dim you'll need to take exposures with the mask on to determine the correct focus. Once you have the right focus remember to take the mask off for the normal exposures ;).

Indeed, the masks are cool. I just tried making one and using it, and it worked great in my test environment -- it might or might not work well for the original asker, though... but if a bright star can be found, I could totally imagine it helping.
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lindesDec 3 '10 at 21:22

Autofocus using some bright/contrasty point at infinity, switch to manual and don't touch the focus any more (still it's a good idea to verify your focus between shots).

Focus manually (again using some bright point; most of the cameras will confirm focus, if it agrees with you, this can be helpful, but don't rely on it).

Focus using the focusing scale (beware that the teles have a long way between last indicated distance and infinity). It's best to check beforehand if your focus scale is accurate at all focal lengths if you're using a zoom lens.

Let the autofocus "saw" and when it can't find anything to focus on, it should settle at infinity, now switch to manual and take the shot. Verify this behaviour in good conditions.

Use Live View and on-screen zoom for focusing if your camera supports it (there has to be something on your picture, right?).

Take the shot and verify if your focus is where it should be by zooming on the screen.

If non of this works, it's probably too dark anyway.

You can try some focusing aid systems like Canon's ST-E2, but I wouldn't be sure they're good at infinity and you'll probably fall back to point 4.

Aids like ST-E2 or those built-in in Canon flashes are quite useless when it comes to infinity, but they definitely help in case you need to focus on something a few meters away.
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cheAug 1 '10 at 19:04

A couple things I haven't seen mentioned in answers (though one of these was mentioned in a comment [EDIT: actually, I think the 1st was mentioned, too, I just mis-read it as talking about the focusing window.]):

use a flashlight, spotlight, car headlights, or other form of light (polution ;) to illuminate something that's either in your frame, or a similar distance from what you want in your frame. Focus on that (or on the light source itself -- for what it sounds like you're doing, this could be city lights of a (hopefully-distant) city (though ideally, you wouldn't have any), or... any number of things. [EDIT: and then, of course, turn this light-source off, for your actual exposure.]

Add that, of course, to the focus-once-and-then-leave-it-in-manual technique (or my preferred option -- configure the camera to not focus on half-press, but with the AF-On or some other button; details vary by camera, of course, but I know many SLRs have this option).

Trial and error with wide-open aperture and highest possible ISO is also a good technique, though that's been mentioned already. :)

If your camera supports LiveView, you could try tethering the camera to a laptop, and using Canon's CameraWindow software to get a decent sized image streamed live. It will make it easier to assess the focus. Assuming Canon, of course, but other manufacturers have similar facilities.

I know exactly what you're talking about. The viewfinder is useless in these situations.

What I do is look for the focus indicator on the lens. I switch to manual focus, and then using some object that emits light (phone, iPod touch, wristwatch, etc), set the focus to infinity. Then, I'll take the shot (say, f/4 and 15 seconds, more than 15 seconds and you'll get trails as the stars move). Then I'll check the validity of the focus through reviewing the photo. I realize that it's not an a priori certitude that you have focus, but since we're dealing with digital, you can burn a few frames.

If you're using a tripod, set up your camera, then crank the ISO all the way up (I go 12800 while preparing for star-trail shots) and aperture wide open. Grab several test shots and you should be able to get a good indication as to where your focus point is. Adjust until you hit your proper framing and focus, and then you should be able re-adjust for your intended ISO, exposure, and time values. Just don't reset your focus to auto before you shoot!

Also, if you're shooting into the sky without much or any foreground, infinity is a great bet. Take a shot in the light so you know which end of the focus ring you need to be at to hit infinity, then just compose your shot with your focus manually set there.

Live view is quite useful if you can see stars, zoom the live view on to one of the brightest stars and in manual focus get it as small and round as possible. Autofocus is useless if you want to photograph the night sky...

There is also some software to help with focusing if you tether your camera to a computer. For canon you can use f. ex. Backyard EOS (http://www.backyardeos.com/) or APT (http://www.ideiki.com/astro/)

There are options to make things a little easier; You can also use the depth of field preview button if your camera supports it (normally at the bottom, on the opposite side from the shutter, for Canon bodies). You could also use as small an aperture as possible (f/22 or above) to maximise the depth of field.

Good suggestions. There is so little light available that lens and focus screen combination render the viewfinder as nothing but a black frame. I added a comment to my question, I'm shooting wide open for short shutter speeds so that stars don't begin trailing.
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Canon GangstaAug 1 '10 at 7:53

Another option would be to get to your scene early, focus on your target (either manually or automatically), then, making sure the focus is back to manual mode, leave the camera there on a tripod and don't touch a thing.

Be aware of temperature changes, these can affect the focus point.
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MarcAug 13 '10 at 8:48

They do? I wouldn't have expected this... although it does make sense. Interesting.
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BossykenaAug 13 '10 at 19:06

@Bossykena Temperature has quite a lot of effect on focus. For example for 200mm f2.8 lens has a critical focus zone of 20 micrometers. This is why many astrophotographers use temperature compensated focusers, which correct the focus all the time according to temperature changes.
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OH6KVUAug 10 '12 at 13:09

Most modern DSLRs autofocus use contrast to find an edge and range. If it's too dark... no contrast. I carry a small LED flashlight in my camera bag. Frame / focus with the light, half press to lock focus, recompose and fire. If your light source is too strong (and your not on manual) exposure can be an issue.

To me the best method of focussing is in daylight to find infinity,choose a lens preferably a fixed focal and focus on infinity,then note the focus point on the distance scale,some use tape,but this is messy,I suggest, using a toothpick applying a small point of white paint on the barrel where the focussed point aligns with the distance line. This leaves a 1mm point that is neat and easily seen. Frigging around trying to focus is a pain and is time consuming (many exposures at 2-3 minutes) Zooms may need several tests because the infinity point can change with focal length.

Given that you can't see anything at all through the viewfinder, it seems to me like a lens with a distance scale is essential. An older manual focus prime would be ideal, and cheap (especially in 50mm), though I don't recall how much backwards compatibility Canons have.

I use a device consisting of a lens and an illuminated picture. The picture is in the focal point of the lens, its exact position can be adjusted. When looking through the lens, the picture will appear to be at infinity.

The picture has a few good autofocus points. I select one of them, focus on that, take a trial picture, and then I adjust the focus by turning a screw on the device which moves the picture by a fraction of a millimeter.